Hi,
I'm the developer of the data source based on the Metrics Data Web Service.
We use the data source for several APM environments and have not experienced any unexpected issues so far. From the GitHub stats and some other contacts I know that others are using the data source as well.
Just keep in mind that the Metrics Data Web Service is not throttled in any way, so be careful with queries that might result in responses with huge amounts of data, e.g. when using wildcards. However, in my experience you rather kill your browser before you get the EM in trouble, as the XML SOAP responses get rather large pretty fast.
In case you have any questions, experience issues, or have suggestions, just reach out to me here or on GitHub.
Cheers,
Fabian